by Kevin Johnson, USA TODAY

by Kevin Johnson, USA TODAY

WASHINGTON - By all accounts, Nancy Lanza's enthusiasm for guns prompted her to acquire at least four firearms, three of which were recovered inside a Connecticut school where her 20-year-old son launched an assault that left 20 children and six staffers dead.

Lanza, herself, was murdered by her son, before Adam Lanza set out for the school last Friday.

Yet beyond the horrific act of violence that has revived a heated national discussion about gun rights, Lanza's firearms collection underscores a recurring theme in the gun debate: that new gun sales increasingly involve existing gun owners and that individual gun ownership is not necessarily expanding in the U.S.

An estimated 20% of gun owners possess 65% of the nation's guns, according to a Harvard University survey published in 2007.

A separate review by the General Social Survey, part of the National Opinion Research Center at the University of Chicago, has tracked a slow decline in the portion of Americans who own guns, from 29% in 1980 to about 21% in 2010.

The surveys offer a differing view of gun ownership from some gun rights advocates, including the National Rifle Association and National Shooting Sports Foundation, which have recently talked of an increase in first-time gun owners and waiting lines at NRA-sponsored firearms safety classes.

Representatives of the NRA and the NSSF could not be reached for comment Wednesday. The NRA has announced it will hold a news conference Friday.

"The suggestion that (gun) ownership is expanding is just wrong," said David Hemenway, health policy professor at the Harvard School of Public Health.

Hemenway, one of the authors of the 2007 survey, said the central conclusion of the review was that gun ownership is becoming "increasingly concentrated."

Almost 48% of all individual gun owners reported owning four or more firearms, according to the survey. What is not entirely clear, Hemenway said, is what is driving the trend.

"It's shocking that we don't have better information," Hemenway said. "We don't know as much as we should."

Last year, an analysis of the General Social Survey findings by the Violence Policy Center, an advocacy group for stricter gun control, attributed the ownership decline to a variety of reasons, including the aging of the existing gun owning population - primarily white males - and the prevalence of single-parent homes headed by women. The center's analysis also showed that one out of 10 females owned a gun in 2010.

Nancy Lanza's status as a divorced, single mother represents a departure from the multiple gun-owner profile.

Otherwise, Lanza's personal information appears to track the surveys' major findings and characteristics of other owners of multiple firearms.

Bradley Buckles, a former director of the Bureau of Alcohol Tobacco Firearms and Explosives, said the weapons traced to Nancy Lanza are "remarkably ordinary" among gun owners.

"The handguns (the Glock and Sig Sauer) are both very popular," Buckles said.

"Even the Bushmaster rifle (the primary weapon in the attacks) is something you would see anywhere," he said. "There are millions of these kinds of firearms out there."